Not Applicable
Not Applicable
1. Field of Invention
This invention relates generally to methods and apparatus for use in the manufacture of vehicle tires. In particular, this invention relates to methods and apparatus for the positioning of a green tire carcass on a shaping drum. More particularly, this invention pertains to
2. Description of the Related Art
In the manufacture of vehicle tires, one process operation includes positioning of a green tire carcass on a shaping drum whereupon the carcass is inflated to a generally desired toroidal shape. The green tire carcass normally is of a generally hollow cylindrical geometry having a non-extensible bead ring secured internally of each of the opposite ends of the carcass. The shaping drum of the prior art includes first and second generally cylindrical mandrels which are disposed on opposite sides of a centerplane oriented perpendicular to the longitudinal centerline of the drum. This longitudinal centerline also defines the rotational axis of the drum. The mandrels of a shaping drum are designed to engage the bead ring-containing opposite ends of the carcass and thereby hold the carcass centered on the drum relative to the centerplane and concentric with respect to the rotational axis of the drum.
In the present embodiment, each of the mandrels is of the radially expansible type, that is, each mandrel comprises a plurality of segments which are disposed radially about the rotational axis of the drum and which collectively define generally the outer circumference of an annular receiver for one of the bead rings of the carcass. The segments of each mandrel are radially moveable relative to the rotational axis of the drum for locking the bead rings of the carcass to the drum and are laterally movable to permit initial selection of the spacing between the bead rings as the carcass. and adjustment of their lateral spacing as the carcass is radially expanded to define a green tire.
For proper functioning of the shaping drum and true rotational dimensioning of the carcass into a vehicle tire, it is important that the carcass initially be positioned precisely centrally of the shaping drum both radially of the drum and laterally of the centerplane of the drum so that upon inflation of the carcass toward a toroidal geometry, all parts of the carcass move or expand uniformly with respect to one another, thereby ensuring uniformity of symmetry of the expanded carcass, as well as uniformity of distribution of the material of construction of the carcass, and ultimately, uniformity of the radial and lateral dimensions and material distribution of the finished tire.
A typical green tire carcass for an automobile will weigh 35-50 pounds or more and is relatively flimsy. Obviously, a green carcass for a truck tire, or an off-the-road (OTR) tire, will be considerably heavier and more difficult to manipulate. Accordingly, loading of the carcass onto a shaping drum is difficult in several aspects. For example, manually placing the carcass onto the drum from one end of the drum, that is xe2x80x9cthreadingxe2x80x9d of the carcass initially onto one end of the drum and further moving the carcass toward the lateral centerplane of the drum is difficult in that the carcass tends to bend, twist, collapse and/or sag due to gravity, from its open cylindrical geometry when lifted by an operator or a mechanical transfer device. After the carcass has been initially threaded onto the drum, there remains the problem of completing the centering the carcass relative to the lateral centerplane of the drum so that the bead rings are disposed on opposite sides of, and equidistantly from the centerplane of the drum and equidistant radially about the rotational axis of the drum. These and other positioning efforts are frustrated by the tendency of the carcass to xe2x80x9csagxe2x80x9d under the effects of gravity thereby impeding the radial centering of the carcass relative to the longitudinal centerline of the drum before, or as, the bead rings become locked to the mandrels of the drum. Failure to center the carcass both radially and longitudinally of the shaping drum can result in non-uniform distribution of the material of the carcass, hence of the finished tire, with the result that the finished tire is unacceptably xe2x80x9cout of roundxe2x80x9d and must be scrapped.
In accordance with one aspect of the present invention there is provided improved means for centering of a green tire carcass on a shaping drum. xe2x80x9cCenteringxe2x80x9d as used herein and unless otherwise stated or obvious from the context of its use, includes positioning of the bead ring-containing opposite ends of a carcass substantially equidistantly from the centerplane of the drum and substantially radially equidistant from, and substantially concentric about, the rotational axis of the drum. In one embodiment, the shaping drum includes first and second pluralities of lateral positioning shoes disposed about the outer circumference of the drum, these pluralities of shoes being disposed on opposite sides of the lateral centerplane of the drum, and first and second pluralities of bidirectional (radial and lateral) positioning wheels, the pluralities of wheels also being disposed about the outer circumference of the drum, on opposite sides of the lateral centerplane of the drum, and between respective ones of the pluralities of shoes and the lateral centerplane of the drum. These shoes and wheels are selectively positionable laterally and radially of the drum.